1. Field of the Invention
The invention relates to a process for producing loose fill packing bodies in the form of spherical segments, having a surface that is convex on the outside and concave on the inside, and to the granules formed thereby.
2. Prior Art
Such packing bodies in the form of spherical segments are known as "loose fill" and are widely used as packing material for items that are to be shipped.
The known packing bodies have the disadvantageous property of being produced from plastic material--such as polystyrene or other polymerization products of styrene, such as a benzene derivative. The packing bodies made of the noted plastic material can be disposed of after use only with difficulty. Especially from the standpoint of ever-increasing awareness of the environment and environmental protection, this is perceived to be a profound disadvantage.
To produce the known loose fill from plastic, a process known from U.S. Pat. No. 3,961,000 is used, in which plastic granules of expandable polystyrene are mixed with additives such as bubble formers, coloring pigments or the like. In a drum, a bubble former is applied to the surface of the plastic granules. Next, these granules are fed into an extruder. The plastic plasticizes as it travels through the extruder, and because of the difference in speed over the cross section of the composition, it emerges from a forming opening in a state in which it has a curved surface. The plastic is cut off directly at the forming opening--even before considerable expansion has occurred. In a first expanding operation, the cut-off plastic particles expand into a specialized three-dimensional shape with a surface that is convex on the outside and concave on the inside. After a certain period in storage, the plastic particles, which are in their first stage of expansion, are subjected to hot steam in a secondary expansion unit and are expanded once more.
U.S. Pat. No. 4,627,947 discloses a process for producing loose fill from plastic having a convex outer surface and a concave inner surface, in which the plastic is fed into an extruder from a fill hopper via an extruder worm. Here the plastic material is drawn into a chamber between the extruder worm and a liner, which in the material intake zone of the extruder is provided with longitudinal grooves. The plastic material, which is plasticized over the course of the extruder, emerges from a forming opening of the extruder with a curved surface, because of the speed difference prevailing across the forming opening. The resultant plastic skein is cut off directly at the forming opening.
U.S. Pat. No. 4,863,655 discloses the use of starch as a basic material for producing a biodegradable packing material. Here, starch having at least 45% by weight of amylose is extruded, and in the extruder, a temperature of approximately 150 to 250.degree. C. prevails. With the process described in this patent, it is possible to make only large-volume "starch blocks", such as insulation plates, in which the size of bubbles in the expanded starch material is relatively large. Moreover, the diameter of these bubbles fluctuates considerably. Accordingly, it is not possible with this process to produce pourable packing bodies in the form of spherical segments; the typical diameter of such "loose fill" packing bodies is approximately up to 3 cm. Given these small dimensions, the bubble size must naturally be substantially less than in the above cases of large-volume starch blocks, to assure solidity of the "loose fill" bodies. Even a few large bubbles in these small packing bodies reduce their stability, and even at an extremely small load causes them to break. It should also be noted that relatively large bubbles especially in the vicinity of the edge of the "loose fill" bodies having a convex outer and concave inner surface--leads to a considerable "danger of crumbling" in this peripheral region, so that the continuous friction during shipping produces a fine "snow" by abrasion, which is deleterious to the packing quality.